O'Neill, Eugene:

$1,750 · Offered by William Reese Company

A TRILOGY: MOURNING BECOMES ELECTRA. Uncorrected original page proofs of the first edition, text printed on rectos only. The configuration in three parts underscores the emphasis in this format on the "trilogy," as does the emphasis implicit in the title-leaves: in the published form, the placement of 'A Trilogy' and 'Mourning Becomes Electra' were reversed. Uncommon in this format.

Found via Rare Books Intel, a search across rare-book dealers, auction houses and marketplaces worldwide.